About sharing the source code. If the game will be released as open source, it may gives push to creating new games in Oberon, and may not. It's hard to say. In any case that is
slenkar's wish - as he decides.
I'm not sure that open source will help to someone to venture to help slenkar in development of the game. I'm not sure that the games in Oberon will be developed massively, for Speccy or not. As you see, parallel with development a game itself, an Oberon developer must improve development tools, etc. It's a way not for anyone.
That's why the work of
slenkar to some extent unique. Excellent that we see something written in Oberon and looks nice as the game. Bravo!

Dear
slenkar!
All you have done is you develop the first game in Oberon for Speccy! Respect!
And indeed the game is very pretty. You and me know that graphic is based on GrTiles,
and cannot be so good as maybe some players are waiting. It's not a problem of the
first game written in Oberon for Speccy.
I would be glad to help you to port the game to other platforms - like Win32/Win64, Linux
and DOS. What do you think about something like Android and iOS? It's highly possible
with Gardens Point Component Pascal (may generate Java bytecode .class'es), or the same
Ofront (as I know, iOS use Objective C that is superset of C),
but it may requires a lot of experimentation.
I liked your game and there are some thoughts.
- I understand what beating of the monsters need some knowledge about different types of attacks.
And maybe, except evils, must be positive roles (or hunting at something like gold or treasures, potions with elixir, etc. All we need - just to have enough memory for this). 
- Already moved units may be differ (by color or by other tile) from unmoved (to see better - who can be still moved).
- I found key E - "End of move" by searching. Not bad before playing to show all control to a player.
- Kempston Mouse support for game like this is very useable.
But it's my work, probably, - to add KM to module ZXDev/Lib/Control.
What to do in level after killing of all Orcs and Goblins?

The gameplay looks some incompleted, and I hope to play in full version of the game and have fun!
I believe that XDev with good set of libraries will propose to a programmer (especially to a newbie) a possibility of a very simple and easy development, and this is important. In this sense, language Oberon virtually no competition.
And I guess, while you've developed the game, you like Oberon as I like it. Then, please, let us know what are your plans for the future? Whether they are related to Oberon technologies?
slenkar, if you wish, you can write an article (or paper) about the process of the game development in Oberon language. And I can help to translate the article to Russian language - to share experiences among ZX Spectrum and Oberon communities. And you'll get the glory and honor.

I wish continued success!